1. Field of the Invention
The present invention relates to the field of power electronics, and more particularly, to an isolated power converter without any auxiliary winding and a switching power supply using the same.
2. Description of the Related Art
Isolated power converters are widely used in various kinds of off-line power supply systems. An isolated power converter typically comprises primary side circuit and secondary side circuit, which are isolated from each other by a transformer with a primary winding and a secondary winding.
The isolated power converter controls a current through the primary winding by turning on and off a power switch, so as to output a substantially constant voltage and/or current in the secondary side circuit. For the purpose of power switch control, feedback values related to an output voltage or other parameters of the power converter are required. In the prior art, some isolated power converters obtain the feedback values by employing an auxiliary winding in the transformer. However, manufacture process of the auxiliary winding is complicated, which would result in rise in cost and a high manufacturing effort. In addition, the auxiliary winding has a large size, so the isolated power converter with an auxiliary winding occupies quite some area on the circuit board and lead to a large size of the circuit board. Meanwhile, the auxiliary winding may introduce EMI to the circuit.